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Ultimate state lines at different suction levels of the optimum compacted (opt.) and wet of optimum compacted (wet) specimens.
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An experimental study has been carried out using a new resonant column torsional shear cell to investigate the small strain behavior of an unsaturated compacted silty sand. The device, recently developed at the Dipartimento di Ingegneria Geotecnica di Napoli (Italy), is fitted for controlled-suction testing using the axis-translation technique. B...
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... However, limited research has been conducted to study the small-strain stiffness behavior of unsaturated high-plasticity soils using laboratory measurements. Mancuso et al. [9] performed suction-controlled resonant column-torsional shear tests on silty sand to analyze the effect of suction and soil fabric on small-strain stiffness. The results indicated that small-strain stiffness increased with suction and mean net stress. ...
Understanding the hydromechanical characteristics of compacted soils is essential as these soils are commonly encountered in several geotechnical structures. The present experimental study evaluated the effect of suction and saturation on the shear and volumetric deformation characteristics of compacted high-plasticity clay. The soil suction values were obtained using filter paper and chilled-mirror hygrometer tests, and small (< 0.001%) to large (> 0.1%) strain dynamic responses were analyzed using a series of bender element and cyclic simple shear tests. Additionally, the volumetric deformation characteristics were evaluated using swell pressure and double oedometer tests. Experiments were conducted on the compacted specimens of Nagpur cohesive soil with varying degrees of saturation (10–95%) and matric suction values (ranging from 52 to 97,930 kPa). The shear strength under static loading increased from 182 to 389 kPa, the stiffness under large-strain dynamic loading increased from 5492 to 10,245 kPa, and collapse potential increased by almost 16 times with the decrease in as-compacted degree of saturation to 50%. Afterward, their values decreased with further reduction in saturation. By contrast, the small-strain shear modulus increased from 19.1 to 65.2 MPa and swell pressure increased from 10 to 212 kPa continuously with the increase in initial matric suction and reduction in the degree of saturation. These experimental findings challenge the conventional assumptions regarding unsaturated clays, emphasizing the consideration of compaction state and microstructural arrangements into the analyses of the hydromechanical response of compacted clays.
... The influence of suction on the stiffness of soils is regulated by bulk water or menisci water effects. Bulk water regulated behaviour prevails for suctions less than the air-entry value; and with increasing suction the soil response shifts to menisci-water regulated behavior (Mancuso et al., 2002). ...
This paper investigates degrees of saturation and magnitudes of cyclic shear stress for which principal stress rotation may have a significant effect on the resilient response of a railway formation material. Advanced cyclic triaxial and hollow cylinder soil element tests in apparatus equipped with high accuracy local instrumentation were carried out on a clay (11%) sand mixture. The results show that the resilient stiffnesses measured in the cyclic triaxial apparatus (without principal stress rotation) and the HCA (with principal stress rotation) increased by a factor of about 6 as the degree of saturation decreased to about 45%. In saturated conditions, increases in the magnitude of cyclic shear stress were found not to have a major effect below a certain cyclic shear stress threshold, but when the cyclic shear stress threshold was exceeded significant stiffness degradation occurred. The cyclic shear stress threshold in free-to-drain conditions was similar to the cyclic shear stress in the soil immediately below a ~ 0.3m deep ballast bed, but comfortably greater than the cyclic stress at a depth of ~1m below the sleeper base. In undrained conditions, the cyclic shear threshold was generally similar to the cyclic shear stress at a depth of ~1m below the sleeper base. RÉSUMÉ : Cet article étudie les degrés de saturation et les amplitudes de la contrainte de cisaillement cyclique pour lesquelles la rotation de contrainte principale peut avoir un effet significatif sur la réponse élastique d'un matériau de formation ferroviaire. Une série d'essais cycliques avancés d'éléments de sol triaxiaux et cylindriques creux dans des appareils équipés d'une instrumentation locale de haute précision a été réalisée sur un mélange de sable argileux à 11%. Les résultats montrent que les raideurs élastiques mesurées dans l'appareil triaxial cyclique (sans rotation de contrainte principale) et le HCA (avec rotation de contrainte principale) ont augmenté d'un facteur d'environ 6 lorsque le degré de saturation diminuait à environ 45%. Dans des conditions saturées, les augmentations de l'amplitude de la contrainte de cisaillement cyclique ne se sont pas avérées avoir un effet significatif en dessous d'un certain seuil de contrainte de cisaillement cyclique, mais lorsque le seuil de contrainte de cisaillement cyclique était dépassé, une dégradation significative de la rigidité s'est produite. Le seuil de contrainte de cisaillement cyclique dans des conditions de drainage libre était similaire à la contrainte de cisaillement cyclique dans le sol immédiatement en dessous d'un lit de ballast d'environ 0,3 m de profondeur, mais confortablement supérieur à la contrainte cyclique à une profondeur d'environ 1 m sous la base de la traverse. Dans des conditions non drainées, le seuil de cisaillement cyclique était généralement similaire à la contrainte de cisaillement cyclique à une profondeur d'environ 1 m sous la base de la traverse.
... Elastic modulus at finite strain (∼ a few %) is a fundamental soil property describing soil deformation induced by mechanical and environmental loadings. It has been widely observed that the elastic modulus of a soil not only depends on a soil's mineralogy, fabrics, and compaction state but also heavily on the ambient humidity or soil water potential (e.g., Mancuso et al. 2002;Sawangsuriya et al. 2009;Schuettpelz et al. 2010;Khosravi and McCartney 2011;Ng et al. 2013;Lu and Kaya 2014;Han and Vanapalli 2016;Dong and Lu 2017;Dong et al. 2018;Banerjee et al. 2020). Such dependence can alter the soil's elastic modulus from hundreds of kPa to thousands of kPa for clayey soils (e.g., Sawangsuriya et al. 2009;Kaya 2013, 2014;Lu 2018). ...
A soil's elastic modulus is a fundamental property defining the soil's reversible stress-strain relation under mechanical and environmental loadings. It has been observed that a soil's elastic modulus can increase up to several orders of magnitude from fully saturated to dry conditions due to two distinct soil water retention mechanisms: adsorption and capillarity. Adsorption affects interparticle stress through van der Waals and electrostatic attraction and interparticle friction coefficient through water film retained by soil sorptive potential. Capillarity governs interparticle stress through capillary pressure and surface tension. The onset and scaling laws of the two mechanisms depend on the soil properties of specific surface area, pore-size distribution, cation exchange capacity, and soil mineralogy. These mechanisms are unified by a proposed elastic modulus characteristic curve (EMCC) equation. It is demonstrated that the proposed EMCC equation can well describe the moisture-dependent elastic modulus of a wide array of soils. Further, an interrelation among the EMCC equation, suction stress and soil shrinkage curves is established, which can greatly facilitate predicting suction stress from soil shrinkage curves and vice versa, further validating the EMCC equation in capturing soil's hydromechanical behavior. The practical importance of the EMCC equation is demonstrated through prediction of ground heave of various soils due to a hypothetical flooding event.
... In parallel with the development of new techniques for the field measurement of capillary suction (e.g. Mendes et al., 2008), some studies about the small-strain stiffness of unsaturated soils were published by Wu et al. (1989), Quin et al. (1991), Picornell and Nazarian (1998), Cabarkapa et al. (1999), Mancuso et al. (2002), Leong et al. (2006), Vassallo et al. (2007aVassallo et al. ( , 2007b, Ng et al. (2009), Sawangsuriya et al. (2009, Khosravi and McCartney (2009), Biglari et al. (2011Biglari et al. ( , 2012, Khosravi and McCartney (2012), Wong et al. (2014), Zhou (2014), Hasan and Wheeler (2016), Dong et al. (2016) and Dong et al. (2018), among others. In general, these unsaturated stiffness models are an extension of saturated ones and are often based on the introduction of one extra factor that accounts for the partial saturation of the soil. ...
... Some of these models (e.g. Mancuso et al., 2002;Vassallo et al., 2007aVassallo et al., , 2007bLeong et al., 2006;Ng et al. (2009) ;Sawangsuriya et al., 2009) make use of unsaturated stress variables, such as mean net stress, p − u a (wherep is the mean total stress and u a is the pore air pressure) and matric suction, u a − u w (where u w is the pore water pressure) while other ones employ state variables that incorporate the degree of saturation, S r . The latter approach improves accuracy but generally requires a larger number of material parameters. ...
This paper presents a model for calculating the small-strain shear stiffness of saturated and unsaturated fine-grained soils as the product of a dimensionless stiffness index and four individual functions of the mean average skeleton stress, the over-consolidation ratio, the reference saturated void ratio and the degree of saturation. The main element of novelty of the model resides in the introduction of a reference saturated state, which results in a dependency of the small-strain stiffness on the degree of saturation. The reference saturated state is calculated according to a recently published constitutive law that relates the quotient between the unsaturated void ratio and the reference saturated void ratio to the degree of saturation. The model requires only two extra parameters for unsaturated states, i.e. one parameter for the volumetric behaviour and one for the stiffness behaviour. These two parameters may also be correlated to the saturated parameters, which simplifies the calibration of the model. The proposed framework is validated against laboratory experiments on three different materials resulting in generally accurate predictions compared to other published models. The good predictive capabilities and the simplicity of the formulation justify the implementation of the model into numerical codes for the analysis of geotechnical problems.
... Recompacted to the same dry density but at different initial water contents may not be considered as "identical." Some researchers reported that different compaction water contents could induce different inherent soil structures (Ng and Pang, 2000;Mancuso et al., 2002). ...
In this study, the effect of saturation methods on the SWCC (soil-water characteristic curve) values of the soil (matric suction) was investigated. The objectives of this study are making a comparison between the soil saturation methods and the effect of soil saturation methods on the SWCC. The study also makes a comparison between determining of SWCC using (Whatman 42) filter paper method and Mp6 sensor device. The methods that were studied are the saturation by adding water to the top surface of the sample and sample saturation through the capillary by adding water to the bottom of the samples, and the third used method of saturation is by compacting the soil with a predetermined water content to give a certain degree of saturation. The laboratory specimens were used to evaluate the effect of different methods of soil saturation and methods of sample preparation, on the obtained SWCC, also to compare the results of SWCC that were obtained by using MP6 sensor with the filter paper method. The saturation methods adopted and investigated in this study are the top surface water adding, capillary water raise, and compaction of the soil with predefined water content. The wetting and drying of SWCC have been obtained to all the used saturation methods, by using both the MP6 sensor and the filter paper method. The results showed that the samples that were saturated by the capillary method had higher soil water characteristic SWCC values than those saturated by adding water at the top of the sample surface or those prepared by compacting the soil with a predetermined water content. The comparison between the three methods of saturation reveals that the capillary rise saturation gives a higher value than the top surface water top and the variable water content method for both wetting and drying SWCC cases. Also, the top surface water top gives higher magnitude of SWCC than variable water content method.
... The small-strain stiffness of a soil is widely considered to be a fundamental parameter for earthquake engineering and prediction of soil-structure dynamic interactions. Understanding the smallstrain stiffness of soils will lead to accurate prediction and rational interpretation of ground movements in geotechnical designs (Thomann and Hryciw, 1990;Zeng and Ni, 1999;Atkinson, 2000;Mancuso et al., 2002;Rahman et al., 2008). In addition, soil disturbance induced by jack and bore, tunneling, pile driving, machine vibration, active and passive movement of retaining wall, etc., can also be reflected by the variation of soil stiffness. ...
A portable bender element-double cone penetration (BE-DCP) testing equipment, which is invented as a prototype model for measuring the small-strain stiffness (shear wave velocity, Vs) and shear strength of in-situ soft soil deposits (loose sand and soft clay) is developed in this study. The shear wave velocity in two orthogonal directions (Vs-hv and Vs-hh) of the in-situ soils is measured from paired bender elements (BE) installed on the side of the cone shaft. The bender elements are housed in a mechanically controlled sliding block in the shaft which not only protects bender elements while the BE-DCP apparatus is being pushed into the ground, but also ensures a good contact between adjacent soil particles and benders when the target depth is reached. The real-time relationship of the pushing force and penetration depth is recorded by force transducer and laser displacement sensor and graphed in LabVIEW. Based on the cone penetration testing (CPT) theory, two formulas are derived to calculate the shear strength parameters of the in-situ soils. Test results obtained from both the portable bender element-double cone penetration (BE-DCP) testing apparatus and conventional laboratory experiments on Ottawa sand 20/30, four different sizes of Dolomite sands in various packing densities and Kaolinite under different water contents and densities as well as a field testing were compared and validated, indicating that the novel designed portable bender elementdouble cone penetration (BE-DCP) apparatus is robust, fast, and cost-efficient for measurement of small-strain stiffness and shear strength of in-situ soils.
... The evaluation of the water content allows the analysis of the soil's behaviour from a hydrological point of view and the study of the mechanical performance under partial-saturation conditions. Experiments have shown how the degree of saturation affects shear strength, compressibility and stiffness in the range of small strains [6,7]. ...
Monitoring changes in soil saturation is important for slope stability analyses. Soil moisture capacitive sensors have recently been developed; their response time is extremely fast, they require little maintenance, and they are relatively inexpensive. The use of low-cost sensors in landslide areas can allow the monitoring of large territories, but appropriate calibration is required. Installation in the field and the setting up of the monitoring network also require attention. In the ALCOTRA AD-VITAM project, the University of Genoa is involved in the development of a system, called LAMP, for the monitoring, analysis and forecasting of slides triggered by rainfalls. Multiple installations (along vertical alignments) of WaterScout sensors are placed in the nodes of the monitoring network. They provide real-time water content profiles in the shallow layers (typically in the upper meter) of a slope. With particular reference to these measurements, the present paper describes the reliability analysis of the instruments, the operations related to the sensor calibration and the installation phases for the monitoring networks. Finally, some of the data coming from a node, belonging to one of the five monitoring networks, are reported.
... After preparation, the soil specimens were subjected to drying and wetting in suction-controlled apparatus prior to the determination of G 0 . Using a suctioncontrolled resonant column, Mancuso et al. [51] investigated G 0 of a compacted silty sand subjected to isotropic compression at constant suction. They found that G 0 increased with suction. ...
... Equation (B10), which was proposed by Wu et al. [96], used the function H(S r ) to calculate the variation of G 0 with soil moisture condition. Mancuso et al. [51] proposed Eq. (B11), in which parameter b controls the increase rate of G 0 with increasing suction; r is the ratio of shear modulus at a very high suction and (G 0 ) s* . Han and Vanapalli [34] proposed Eq. (B12) to calculate the variation of G 0 with increasing suction and degree of saturation. ...
An unsaturated soil is a three-phase material that is ubiquitous on the earth’s surface. The fully saturated and completely dry states are just two limiting conditions of an unsaturated soil. The state and properties of unsaturated soils can change significantly with external loads, weather conditions and groundwater level. Proper modelling of the state-dependent behaviour of unsaturated soils is crucial for analysing the performance of almost all civil engineering structures. So far, there are many unsaturated soil models and several relevant review papers in the literature. None of the existing review papers, however, focused on the state dependency of unsaturated soil behaviour. Moreover, some aspects of soil behaviour have not been reviewed, including small strain stiffness, dilatancy and stress-dependence of water retention curve. In the current review paper, the state dependency of unsaturated soil behaviour is reviewed, with a particular attention to the three missing parts. The review is carried out in a unified and relatively simple constitutive framework, which adopts a three-by-three compliance matrix to link incremental volumetric strain, deviator strain and degree of saturation to incremental mean net stress, deviator stress and suction. All of the nine variables in the proposed three-by-three compliance matrix have clear physical meanings and can be measured through compression, shearing and water retention tests. Theoretical models based on other constitutive stress variables can be also converted to this framework by matrix transformation.
... Procter and Khaffaf (1984), Ansal and Erken (1989), Boulanger et al. (1998), and Zhou and Gong (2001) found dynamic loading frequency has a significant impact on undrained dynamic performance of clay. Mancuso et al. (2002) studied the effects of suction and fabric on soil behavior under the small strain by controlledsuction resonant column-torsional shear tests. Results showed a S-shaped initial shear stiffness versus suction variation. ...
Dynamic modulus of elasticity and damping ratio are two important parameters of dynamic properties of soil. These two parameters were extensively studied in the laboratory. However, there has been little research on these two parameters of the unsaturated red clay which is located in the southwest of Hunan, China. With the rapid development of high-speed railway in China, it is urgent to identify the dynamic properties of the unsaturated red clay to provide reference for the civil engineering industry. In this paper, DDS-70, an electromagnetic type dynamic tri-axial testing system, was used to study the effects of water content, dry density, confining pressure, over-consolidation ratio and loading frequency on dynamic elastic modulus and damping ratio of unsaturated red clay. The result shows that within the phase of small strain the influences of water content, dry density, confining pressure, over-consolidation ratio and loading frequency on dynamic modulus of elasticity are obvious. Dynamic modulus of elasticity increases with the increase of dry density, confining pressure and over-consolidation ratio under the same strain, whereas dynamic modulus of elasticity decreases with the increase of water content and loading frequency. Moreover, the effects of these factors on damping ratio are also significant during the phase of small strain. With the increase of strain, damping ratio increases with the decrease of dry density, confining pressure and over-consolidation ratio under the same dynamic strain. There is no clear relationship between damping ratio and loading frequency. It is concluded that the influence of above factors on the dynamic modulus of elasticity and damping ratio is significant.
... It is noted that precise control of suction 111 in the whole range mentioned above is crucial when considering unsaturated coarse-grained 112 soils. For fine-grained soils, on the other hand, the AT method was deemed to be good enough 113 to cover parts of the water retention curve in dynamic testing [20,21]. Therefore, the 114 combination of two suction control approaches was considered in this research to cover all 115 possible degrees of saturation from fully saturated to relatively dry state for a medium sand. ...
... Although there is a consensus on the stiffening effect of suction on soil 397 structure and hence the enhancement of shear modulus, various increasing trends have been 398 reported for various soil types and testing conditions. A sigmoid trend, for example, was 399 reported for variations in small strain shear modulus with suction by Mancuso et al. [20] as 400 well as Khosravi and McCartney [37]. Ng et al. [38] and Hoyos et al. [39], on the other hand, 401 ...
... The merit of the new set of results compared to the previously reported ones (e.g. 446 [20,32,43]) is that the G values are available in the main points of water retention curve in this 447 study and thus a clear SWRC-based interpretation can be put on the results. On the other hand, 448 D generally reduces with ψm to a minimum and then increases again (Fig. 11b). ...
A cyclic simple shear device was modified for testing coarse-grained soils at unsaturated conditions. A combined methodology of controlling suction for the practical range of coarse-grained soil water retention curves was adopted. Water head control method was used to accurately control suction within capillary and transition zones of such soils. The axis translation technique, on the other hand, was employed as a complementary approach to reach higher suction values within residual zone. In order to evaluate the performance of the new setup, independent cyclic tests were carried out at various initial suctions including all key points and zones along the primary drying path. The analyses of cyclic stress-strain curves revealed an S-shaped trend of shear modulus against suction, where the peak occurs after residual suction. The merit and necessity of recent modifications were highlighted through comparing shear modulus obtained from constant-suction tests with that of constant-water content experiments.
